1. Orbitals and Electron configurations

2. Pauli Exclusion Principle
Reference: pg. 203
The Pauli Exclusion Principle states that each electron (waveform) has a unique set of quantum numbers
No two electrons can have the same values for all quantum numbers
Kinda like how each apartment in a building has only one address
Q: How many electrons will fit in shell 5 (i.e. what is the max. shell pop-ulation for n=5)?

3. Electrons in n = 5 shell
Q - what is the maximum shell population of n = 5
ms = 1/2
ms = -1/2
l = 0(s)
ml = 0
ms = 1/2
ms = -1/2
ml = 1
ml = 0
ml = -1
ms = 1/2
ms = -1/2
l = 1(p)
ms = 1/2
ms = -1/2
n = 5
l = 2(d)
A - 50
( )
l = 4 has 9 orbitals: it has 18 electrons
or 2(5)2 = 50
l = 3(f)
l = 4(g)

4. Filling orbitals with electrons: film
Movie (10 minutes) (at t=20)
0 - 3: review
Bohr explained some observations. However, he failed in other areas.
Later we will look at probability distributions (Heisenburg’s uncertainty principle and orbital shapes). For now we will examine how electrons fill orbitals.
3 - 6: filling orbitals with electrons
We will see that electrons are placed in the lowest energy level possible.

5. Electron Configurations
Electrons are placed in the lowest energy levels that are possible while still following the Pauli exclusion principle
Hund’s rule states that the electrons should be spread within a subshell as much as possible
To know which subshells are lowest in energy refer to fig (arrows going up to left) or fig …

6. Electron Configurations
Electrons fill the lowest energy levels first (calcium shown) 4d
E N E R G Y 5s 4p 3d 4s 3p 3s 2p 2s 1s
Read section 6.7 (pg ). Do PE 5,6

7. Shorthand electron configurations
Recall that we can indicate position of electrons via orbital diagrams or electron configurations.
Fitting 100 or more electrons into this pattern becomes cumbersome.
We can write shorthand electron configurations…
Read remainder of 6.7 (pg ). PE 7.

8. Shorthand electron configurations
Because electrons fill orbitals in a regular pattern, we can shorten the work of writing electron configurations by using the preceding noble gas as a template
We write the highest shell last to indicate the “valence electrons” - i.e. those furthest out (involved in bonding and chemical reactions)
We can represent shorthand electron configurations of the noble gasses 2 ways: E.g. Ar = 1s22s22p63s23p6 = [Ne]3s23p6 = [Ar]
Use [Ne]3s23p6 for this course
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